As shown in FIG. 1, a conventional GaN light emitting diode has a structure comprising a substrate 1, a buffer layer 2 formed on top of the substrate 1, an N-type GaN layer 3 formed on top of the buffer layer 2, a light emitting stack layer formed on top of the N-type GaN layer 3, and a P-type GaN layer 5 formed on top of the light emitting stack layer 4. As shown in FIG. 2A, using the inductively coupled plasma-reactive ion etching (ICP-RIE) dry etching technique, the structure of FIG. 1 is etched downwards through the P-type GaN layer 5, light emitting stack layer 4, and a portion of the N-type GaN layer 3 to form an N-Metal forming area 6 of depth about 10,000Å. As shown in FIG. 2B, a transparent conductive layer (TCL) 7, which can be used as a P-type ohmic contact, is formed on top of P-type GaN layer 5. As shown in FIG. 2C, an N-Metal 8, which can be used as an N-type ohmic contact, is formed on N-Metal forming area 6. As shown in FIG. 2D, a bump pad 9 with a diameter about 100 um is formed on both TCL 7 and N-Metal 8. A conventional GaN LED can be manufactured by following the aforementioned steps.
In the aforementioned steps, TCL 7, N-Metal 8, and bump pad 9 are formed by electronic gun vapor-phase steam electroplate technique, or other similar techniques, such as heat-resist vapor-phase steam electroplate, or splash vapor-phase steam electroplate. The TCL 7 is made of Ni/Au of size about 50 Å/50 Å, or other materials, such as NiCr/Au, or Ni/Aube. The N-Metal 8 is made of Ti/Al of size about 150 Å/1500 Å, or other materials, such as Ti/Al/Ti/Au (150 Å/1500 Å/2000 Å/1000 Å), or Ti/Al/Ni/Au (150 Å/1500 Å/2000 Å/1000 Å). The bump pad 9 is made of Ti/Au (150 Å/20000 Å), or other materials, such as, Ti/Al/Ti/Au (150 Å/1500 Å/2000 Å/10000 Å), or Ti/Al/Pt/Au (150 Å/1500 Å/2000 Å/10000 Å).
However, the structure and its ohmic contact of the conventional GaN LED manufactured with the aforementioned method have a drawback. Because the material used for TCL 7, Ni/Au, has a low photo-penetrability, it is necessary to be very thin (about 50 Å) to have a photo-penetrability of 70%. However, at this thickness, the electrical conductivity decreases. Thus, it is difficult to improve the operating voltage (Vf) and the illumination (Iv) of the conventional GaN LED effectively. To solve the problem, a new structure needs to be devised.